/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.getopt.util.hash;


/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based lookup. See
 * http://murmurhash.googlepages.com/ for more details.
 * <p>
 * The C version of MurmurHash 2.0 found at that site was ported to Java by Andrzej Bialecki (ab at
 * getopt org).
 * </p>
 */
public class MurmurHash
{
    public static int hash(byte[] data, int seed)
    {
        int m = 0x5bd1e995;
        int r = 24;
        int h = seed ^ data.length;
        int len = data.length;
        int len_4 = len >> 2;
        for (int i = 0; i < len_4; i++)
        {
            int i_4 = i << 2;
            int k = data[i_4 + 3];
            k = k << 8;
            k = k | (data[i_4 + 2] & 0xff);
            k = k << 8;
            k = k | (data[i_4 + 1] & 0xff);
            k = k << 8;
            k = k | (data[i_4 + 0] & 0xff);
            k *= m;
            k ^= k >>> r;
            k *= m;
            h *= m;
            h ^= k;
        }
        int len_m = len_4 << 2;
        int left = len - len_m;
        if (left != 0)
        {
            if (left >= 3)
            {
                h ^= data[len - 3] << 16;
            }
            if (left >= 2)
            {
                h ^= data[len - 2] << 8;
            }
            if (left >= 1)
            {
                h ^= data[len - 1];
            }
            h *= m;
        }
        h ^= h >>> 13;
        h *= m;
        h ^= h >>> 15;
        return h;
    }

    /* Testing ...
    static int NUM = 1000;

    public static void main(String[] args) {
      byte[] bytes = new byte[4];
      for (int i = 0; i < NUM; i++) {
        bytes[0] = (byte)(i & 0xff);
        bytes[1] = (byte)((i & 0xff00) >> 8);
        bytes[2] = (byte)((i & 0xff0000) >> 16);
        bytes[3] = (byte)((i & 0xff000000) >> 24);
        System.out.println(Integer.toHexString(i) + " " + Integer.toHexString(hash(bytes, 1)));
      }
    } */
    /**
     * Generates 32 bit hash from byte array with default seed value.
     * @param data byte array to hash
     * @param length length of the array to hash
     * @return 32 bit hash of the given array
     */
    public static final int hash32(final byte[] data)
    {
        return MurmurHash.hash(data, 0x9747b28c);
    }

    public static final int hash32(String key)
    {
        //Profiler found String.getBytes() to be main bottleneck, seemingly a common cause for complaint.
        //  Java 7 may improve, see: https://blogs.oracle.com/xuemingshen/entry/faster_new_string_bytes_cs
        return hash32(key.getBytes());
        //So pre JDK7 could try suggestion from here: http://blog.rapleaf.com/dev/2010/04/26/faster-string-to-utf-8-encoding-in-java/
        //      return hash32(fastStringToBytes(key));
    }
}
